The present invention relates to a pulse generation circuit using at least one Josephson junction device and, more particularly, to a pulse generation circuit which can generate an extremely short duration pulse whose duration can be selected as desired, and has a simple circuit arrangement suitable for integration.
Josephson junction devices operable at very low temperatures around the temperature of liquid helium (He) are far superior to conventional semiconductor devices developed on a silicon or GaAs substrate in the aspects of low power consumption and high speed switching operation. Therefore, it would be possible to build a computer by making use of Josephson junction devices as its switching elements or memory elements. For such a high speed computer, it is necessary that circuits such as a memory circuit, a logic circuit and a control circuit be operated with a short access time or a short cycle time, and a timing pulse for fast and accurate operations of the circuits should have short rise and fall times and a short duration.
Difficulty is experienced, however, in attaining such a timing pulse by means of a semiconductor pulse generator under room temperature. If attained, the deterioration of the waveform of the timing pulse is caused by the cable connecting the semiconductor pulse generator with the Josephson junction IC. It is therefore necessary to generate such a timing pulse which is synchronous to a clock current generated by a signal source under room temperature by using the Josephson junction IC.
To meet these requirements, there has been proposed a circuitry in which one gate current path of an interferometer gate circuit is grounded through a Josephson junction and a resistor while a control current path is supplied with an input pulse signal and said one gate current path with a DC gate current. See the paper entitled "A Josephson Ultrahigh-Resolution Sampling System", David B. Tuckerman, Appl. Phys. Lett. 36(12), June 15, 1980, pp. 1008-1010. In the proposed circuitry, a gate current is fed to the Josephson junction when the gate circuit is transferred from the zero-voltage state to the voltage state by supplying an input pulse signal. In the voltage state, the gate current flows through the resistor until the gate current exceeds a threshold current. The flow of the gate current exceeding the threshold current causes the Josephson junction to make a transition to the voltage state and thereby sharply reduces the current flowing through the resistor. Thus, the current flowing through the resistor is picked out as a pulse current. However, since the gate circuit holds its voltage state even when the input pulse is terminated, the next output pulse cannot be produced unless the gate circuit is reset to the zero-voltage state. Therefore, the gate current must be cut off before the supply of each input pulse signal. Non-latching operation of the gate circuit for resetting the gate circuit automatically is impossible because the Josephson junction remains in the voltage state (high resistance state).
A circuit has been proposed by Faris for resetting the gate circuit automatically to the zero-voltage state so as to generate an output pulse in response to each input pulse signal. See the paper entitled "Generation and Measurement of Ultra-Short Current Pulses With Josephson Devices", Sadeg M. Faris, Appl. Phys. Lett. 36(12), June 15, 1980, pp. 1005-1007. This circuit includes a second gate circuit having one of its control current paths connected in series with the control current path of the first gate circuit, the other control current path supplied with a DC bias current and a gate current path connected in parallel with the gate current path of the first gate circuit through a coil. Such circuitry is also not fully acceptable because additional elements such as the second gate circuit and inductor element are needed to reset the gate circuit and the inductor element occupies a substantial chip area which renders the circuitry unsuitable for integration. Furthermore, neither one of the proposed circuit can freely vary the duration of pulses.